Tires for heavy load vehicles, such as trucks and buses, (tires for heavy loads) are required to have characteristics such as wear resistance, cut resistance, and low heat build-up. Under such circumstances, as a rubber composition for a tire for heavy loads, a rubber composition in which carbon black and/or silica is blended in a rubber component having natural rubber as a main component is typically used.
For example, Japanese Unexamined Patent Application Publication No. 2011-57967 discloses a rubber composition for tire treads which is suitable for pneumatic tires for heavy loads, the rubber composition comprising: diene rubber containing at least 50% by mass of natural rubber; silica; a particular carbon black; and a silane coupling agent (claims, paragraph [0031]). Furthermore, in its working examples, Si69 (bis(3-(triethoxysilyl)propyl) tetrasulfide, manufactured by Evonik Degussa) is used as the silane coupling agent. Japanese Unexamined Patent Application Publication No. 2011-57967 describes that both wear resistance and low heat build-up of the tire can be achieved by using a rubber composition having such a constitution.
When the inventors of the present technology investigated into a rubber composition comprising: diene rubber containing at least 50% by mass of natural rubber; silica; carbon black; and a silane coupling agent, using Japanese Unexamined Patent Application Publication No. 2011-57967 as a reference, it was found that, although the obtained tire exhibits excellent wear resistance, if heavy load tires are required to have even higher performances in the future, the cut resistance and low heat build-up of the obtained tire may not be sufficient to satisfy such a requirement.
Further enhancement of characteristics such as wear resistance, cut resistance, and low heat build-up, has been desired for tires for heavy loads to enhance safety, fuel consumption, and the like of heavy load vehicles.